1. Field of Invention
The present invention relates to a projector for displaying color images.
2. Description of Related Art
A projector uses a light modulation device, called a light valve, in order to modulate light according to image signals. A known type of projector for displaying color images uses three light valves corresponding to three colors, red light (in the wavelength region of approximately 580 nm to approximately 700 nm), green light (in the wavelength region of approximately 500 nm to approximately 580 nm), and blue light (approximately 400 nm to approximately 500 nm). In most cases, transmissive liquid crystal panels, reflective liquid crystal panels, or the like are used as the light valves.
It is known hitherto that ultraviolet light having a wavelength shorter than that of blue light (light of approximately 400 nm or less) is a cause of deterioration of the operating characteristics of a liquid crystal panel. In order to prevent this, an ultraviolet cutoff filter is provided to inhibit light having a wavelength of approximately 400 nm or less from reaching the liquid crystal panel.
Although ultraviolet light is cut off by the ultraviolet cutoff filter, the operating characteristics of the projector are sometimes deteriorated due to deterioration of the operating characteristics of a liquid crystal panel for blue light. This phenomenon has become more prominent, in particular, with recent increases in brightness of the light source and increases in efficiency for light utilization of the optical system.
The present invention has been made to at least overcome the above problems in the conventional art, and an object of the invention is to at least provide a technique for inhibiting deterioration of the operating characteristics of a liquid crystal panel, which has been caused by increases in the brightness of images.
In order to solve at least some of the above problems, a projector according to the present invention includes:
a light source;
a wavelength separating optical system for separating light emitted from the light source into light in the plural wavelength regions;
plural light modulation devices provided respectively for light in the plural wavelength regions emitted from the wavelength separating optical system so as to modulate the light in the plural wavelength regions according to a given image signal;
a light synthesizing optical system that synthesizes the light in the plural wavelength regions modulated by the plural light modulation devices; and
a projection optical system that projects the synthesized light emitted from the light synthesizing optical system, wherein a reflecting mirror, having a reflectance of approximately 90% or more for light in the wavelength region of approximately 435 nm or more, and a reflectance for light in the wavelength region of 425 nmxc2x15 nm, that is lower than the reflectance for the light in the wavelength region of approximately 435 nm or more, or a light filter having a transmittance of approximately 90% or more, for light in the wavelength region of 435 nm or more of the light in the plural wavelength regions, and a transmittance for light in the wavelength region of at least 425 nmxc2x15 nm, that is lower than the transmittance for the light in the wavelength region of approximately 435 nm or more, is placed in the optical path from the light source to at least one of the light modulation devices.
Herein, xe2x80x9capproximatelyxe2x80x9d in for example, xe2x80x9capproximately 435 nmxe2x80x9d, or xe2x80x9capproximately 425 nmxe2x80x9d, means that the value of the design wavelength (435 nm, 425 nm) may include a margin of error. While the allowable error range varies depending on the size of the projector or the like, it is generally xc2x13 nm.
As a result of examination of the causes of deterioration of the characteristics of the liquid crystal panel for blue light, it was discovered that the operating characteristics of the light modulation device noticeably deteriorates when light in the wavelength region of 425 nmxc2x15 nm (hereinafter referred to as xe2x80x9clight with a wavelength of approximately 425 nmxe2x80x9d) is applied. Although the cause is not yet clear, it is hypothesized that light with a wavelength of approximately 425 nm has an adverse effect on the material (e.g., polyimide) of an alignment film used to align liquid crystal molecules in the liquid crystal panel, and the material (e.g., ITO) of electrodes used to apply voltage to the liquid crystal. In the above projector, a reflecting mirror, having a reflectance of approximately 90% or more for light in the wavelength region of approximately 435 nm or more, of the light in the predetermined wavelength regions, and a reflectance for light in the wavelength region of approximately 425 nm, that is lower than the reflectance for the light in the wavelength region of approximately 435 nm or more, or a light filter having a transmittance of approximately 90% or more, for light in the wavelength region of approximately 435 nm or more, of the light in the predetermined wavelength regions and a transmittance for light in the wavelength region of approximately 425 nm, that is lower than the transmittance for the light in the wavelength region of approximately 435 nm or more, is provided in the optical path from the light source to the light modulation device. Therefore, it is possible to inhibit light with a wavelength of approximately 425 nm from entering the light modulation device. This can prevent the operating characteristics of the light modulation device from deteriorating. It is preferable that the reflectance of the reflecting mirror for light of approximately 425 nm be approximately 20% or less, and preferably, it should be as low as possible. It is preferable that the transmittance of the light filter for light of approximately 425 nm be approximately 20% or less, and preferably, it should be as low as possible.
Preferably, the reflecting mirror or the light filter is disposed in the optical path in which light in a predetermined wavelength region, including light with a wavelength of approximately 425 nm, of light in the plural wavelength regions is separated by the wavelength separating optical system and enters a corresponding light modulation device. When the reflecting mirror or the light filter is placed at such a position, production thereof is facilitated.
Preferably, the reflecting mirror has a reflectance of approximately 90% or more for visible light in the wavelength region of approximately 415 nm or less, and a reflectance for visible light in the wavelength region of approximately 425 nm, that is lower than the reflectance for visible light in the wavelength region of approximately 415 nm or less. Preferably, the light filter has a transmittance of approximately 90% or more for visible light in the wavelength region of approximately 415 nm or less, of the light in the predetermined wavelength regions, and a transmittance for visible light in the wavelength region of approximately 425, that is lower than the transmittance for visible light in the wavelength region of approximately 415 nm or less.
Since this allows not only light in the wavelength region of approximately 435 nm or more of the light in the predetermined wavelength regions, but also light in the wavelength region of approximately 415 nm or less to be used in the light modulation device, it is possible to prevent the operating characteristics of the light modulation device from deteriorating and to ensure a sufficient intensity of light.